The present invention relates generally to fabrication of objects and prototypes through the sequential deposition of material. More particularly, the invention relates to ultrasonic consolidation.
Conventional machine tool such as lathes, mills, EDM machines etc. use various methods to remove material from a block or billet to produce an object of a desired shape. This process is highly efficient and accurate in many applications, but has shortcomings when certain types of features, such as deep narrow slots, or complex internal features are required. In these situations multiple machine set ups may be required, or conventional machining may be combined with EDM to produce the desired features. In some cases, it may be necessary to produce a casting in order to obtain the desired geometry. The ability to add and remove material on the same machine can address many of these issues, and allow objects to be produced more quickly and efficiently than current methods.
Many technologies are now being marketed to perform additive manufacturing. Generally known as rapid prototyping technologies these include stereolithography, fused deposition modeling, selective laser sintering, laser powder deposition and others. Most of these processes have only been robustly commercialized for use with polymer, wax or paper feedstocks. As a result, they cannot be used commercially, alone or with subtractive processing, to produce objects from engineering metals.
Some researchers have developed techniques to apply metals via welding methods, and to machine away excess material (Prinz, U.S. Pat. Nos. 5,301,415; 5,281,789; and 5,207,371) either using or without a support material (Kovacevic). These systems involve using arc welding, or laser metal deposition (with either powder of wire feedstocks) to deposit molten metal droplets. Another approach is droplet generation by various metal melting and droplet formation techniques (as described by Starrett, Prinz, Chen, Tseng, Visnawathan and others). Incorporating molten metal droplet deposition in such a system presents certain problems, including the presence of high voltage, smoke and fume, eye safety issues, the retention of molten metal etc. associated with welding and foundry operations. These issues have inhibited adoption of welding, laser deposition and other molten metal techniques as a means of adding material to an object prior to or during machining.
As described in U.S. patent application Ser. No. 09/532,432, ultrasonic object consolidation is a technique for performing additive manufacturing which avoids most of the problems associated with other metal deposition methods. The solid state, low energy nature of this process eliminates hazards such as molten metal, high intensity arcs, high power, dust and smoke, etc.
This invention is directed to a practical machine tool for combining material addition via ultrasonic object consolidation, including subtractive techniques for imparting high-dimensional accuracy to a finished object. Broadly, a system according to the invention includes a material supply and feeder, ultrasonic horn, and feedstock cutting device. These components are integrated with a material removal subsystem preferably including a cutting tool and an excess material removal system.
Any metal, plastic or composite material suitable for ultrasonic joining may be employed as a feedstock, and these materials may assume the form of tapes, sheets, wires, filaments, dots or droplets, with the feeding and material cutting components being designed for the specific feedstock employed. The cutting tool for excess material removal may be a knife, drill/mill, grinding tool, laser or other tool capable of accurately cutting the external contour of a cross section of the part being built, and of removing excess feedstock remaining following the application process. The material removal could consist of a vacuum or blower system, chip auger, or other suitable apparatus.
A machine disclosed as part of the preferred embodiment is able to deposit material in one step, and optionally and selectively remove it in another. Through the expeditious combination of deposition and removal, the fabrication of objects of arbitrary shape may be realized. This embodiment of the invention feeds raw material in the form of metal tape to the deposition head, where it is bonded layer by layer in an upward fashion.
In terms of apparatus, a preferred embodiment includes a deposition head for adding raw material mounted adjacent to a device which removes material, both of which move in X-Y-Z motion with respect to a material deposition plane. Both the deposition head and removal device are connected to a Z-carriage which provides a full range of orthogonal motion for both devices using a single motion structure. Motion in the +/xe2x88x92X and +/xe2x88x92Y directions is effected by separate gantry/carriage mechanisms. A movable track carries electrical power and signal lines to and from the moving units. A tool holder permits on-the-fly switching of tool profiles.
In a different embodiment, the material feeder, removal unit, or both may advantageously be mounted on separate multi-axis robots. The robot design may be conventional rotary axis industrial robots, Cartesian robots, or other designs suitable for effecting flexible, programmable motion. Advantages of robotic mounting include the ability to include one or more robots in a single work cell, to separate various functions such as material feeding, material consolidation, and material trimning so as to increase throughput, and to enable incorporation of material feeding, consolidation and trimming into other manufacturing operations. A robotic arm may also be mounted on a gantry type carriage of the type described previously providing the advantages of robotic flexibility over the large travel areas provided by gantry type systems.
Alternatively, the feeder may be mounted relative to a multi-axis mill or other machining center functioning as the removal unit. The object being fabricated may also be fixtured enabling fabrication from the center outward to realize particular advantages such as the minimization of residual stress accumulation. To minimize xe2x80x9cstairsteppingxe2x80x9d the material removal unit may be operative to perform two trimming operations, including a high-speed trimming operation and a contouring trim to provide material increments in two or more directions. The material feeder may include multiple sources to deposit increments in multiple directions, or to fabricate the using dissimilar materials and/or varying thicknesses.